The present invention relates to a reflective plate used in a reflective type display. The invention also relates to a liquid crystal display (LCD) using such a reflective plate. Furthermore, the invention relates to electronic apparatus using such a liquid crystal display.
In recent years, liquid crystal displays have been applied to personal computers (PCs), TV receivers, wordprocessors, video taperecorders, and so on. Meanwhile, such electronic apparatus have been required to have more functions. Also, there is a demand for miniaturization, power saving, and lower costs. For these purposes, there is a demand for a reflective type liquid crystal display that displays a liquid crystal image by reflecting externally incident light without using backlight.
It is important for such a reflective type liquid crystal display that an image is created by making efficient use of externally incident light without using backlight.
As shown in FIG. 16A, a reflective film 4 used in a reflective type liquid crystal display is placed below a liquid-crystal layer 38 and reflects incident ambient light. A part of the ambient light is reflected by the surface of an upper substrate 2; the remaining ambient light passes through the upper substrate 2 and the liquid-crystal layer 38 and is reflected by the reflective film 4. Therefore, if the direction of reflection of light at the surface of the upper substrate 2 is identical with the direction of reflection of light at the reflective film 4, the light source is seen to overlap the image on the liquid crystal display. This presents the problem that the image is not viewed comfortably, i.e., the visibility is deteriorated.
Accordingly, an arrangement of a pattern consisting of a multiplicity of irregularities 3 on the surface of the reflective film 4 as shown in FIG. 16B has been proposed. As shown in FIG. 16C, the irregularities 3 reflect incident light. Where light incident on the reflective film 4 is reflected by the irregularities 3, the LCD screen can be visually observed using light not directed in the same direction as those components of the scattered light which are regularly reflected at the upper substrate 2. It is possible to observe the LCD screen from a direction different from the light regularly reflected off the upper substrate 2. This improves the visibility.
As shown in FIG. 17B, the angle of reflection α can be adjusted by appropriately selecting the tilt angle at the surface of convex portion 3a. The light not directed in the same direction as the light regularly reflected from the surface of the upper substrate 2 can be guided to the view position.
However, if the surfaces of the irregularities 3 are formed at the same tilt angle, and if the irregularities are uniform in shape over the whole reflective film 4, it follows that incident light is reflected even from directions not used for observation of the LCD screen. Light is reflected even in wasteful directions. This deteriorates the efficiency of utilization of light.
In particular, as shown in FIG. 17A, if each irregularity 3 is made to have a minute area, and if light incident normal to the reflective film 4 spreads within angle α, the light reflected by the reflective film 4 is reflected to regions II, III, and IV (FIG. 17A) excluding both-side regions I that light reflected from the reflective film 4 does not reach at all.
With respect to the regions II of these regions, only light reflected from parts (αL and αR, respectively) of the reflective film 4 reaches the regions II. With respect to the region IV, light reflected from the whole reflective film 4 reaches the region IV. However, the contrast of the LCD screen is impaired due to regular reflection from the upper substrate 2. This makes it difficult to recognize the image.
With respect to the regions III, light reflected from the left side αL and the right side αR of the reflective plate 1 reaches these regions III. Since these regions are not affected by regular reflection from the upper substrate 2, the image on the LCD screen can be recognized.
Therefore, it is desirable to use the regions III as an effective field of view area that is a viewable LCD screen.
However, these effective field of view areas III are formed like a doughnut around the region IV located at the center. We now consider a case in which these effective field of view areas are used for cellular phones. In the case of a reflective LCD screen, if there is a light source incident normal to the upper substrate, it is impossible to view the LCD screen from just above. Therefore, one inevitably views the screen at an angle. At this time, if he or she views from a sideways direction, observation of other persons is facilitated. Consequently, it is natural that he or she views the screen from obliquely above or below as shown in FIG. 14. In order to form an exit region obliquely above or below, it is necessary to impart directivity to the reflective surface of the reflective plate such that reflected light is collected onto the effective field of view areas III.
Techniques for tilting the reflective surface of a reflective plate to impart reflectivity to the reflected light have been known. These related art techniques shift light reflected to the region IV to the regions I that the reflected light does not reach at all, and are not intended to collect the reflected light onto the effective field of view areas III. In consequence, the efficiency of utilization of light is not improved.